Kat is still Exploring with the Camera and is encouraging us to look for opposing lines and how they lead the viewer's eye into and around the photo. Her excellent, informative post is here. So I wandered through my archives (I love doing that when I have the time!) and found a few examples of what I think represent opposing lines.
Architecture is a great place to notice opposing lines - this pic of a glass roof has it all - angled, straight and intersecting to lead your eye through and back through the photo.
Another ceiling (in Las Vegas) filled with curving lines - I'm less sure if these would be considered opposing lines, but I like the shot, so.....it's in. (Kat, let me know if it's not quite what you meant.)
The new City Center development in Las Vegas fits the theme I think with the strong vertical format but all the horizontal window lines.....
As Kat explains, reflections are a great way to capture opposing lines - here I have the slight waves of the water reflecting a vertical building (in CA).
I always find it so interesting to take Kat's premise or discussion of photographic vision, deconstruct it and explain it so clearly, then wander through my archives to see if I've ever used that principle - usually unknowingly. But, as shown here, even though I might not have been aware of the principle, it is one that attracts my attention occasionally.
Please take a moment to peruse Kat's site (KatEyeStudio) and absorb all the great info she shares. Better yet, join in, the folks are great!